Fuel injection devices for operating an i.c. engine have been generally known for many years. In a so-called common-rail injection system the feeding of fuel into the respective combustion chamber of the i.c. engine is effected by means of injectors. During this process a high injection pressure and precise control of the injection quantity is advantageous because this makes it possible to achieve, on the one hand, a high specific power of the i.c. engine and, on the other hand, a low emission of pollutants.
Control of the injection quantity is effected in this case by means of a closed control loop. The energy stored in the injector is used as a controlled variable as this energy correlates with the injection quantity. By means of a supply unit the individual injectors are then charged and discharged. Under certain conditions, as will be explained in more detail in the description of the figures, it may happen that the calculated energy stored in the injector does not correlate with the injection quantity and so the closed control loop no longer operates in an optimum manner.